Detection of subtly discriminated regions in volumetric medical imaging may be challenging.
One example of detection of subtly discriminated regions is the detection of early ischemic signs in non-contrast computed tomography (NCCT) for acute stroke. In such detection, the main pathology or pathologies of interest may comprise dense vessels (thrombus) and areas of ischemia and infarcts. In some circumstances, dense vessels may be challenging to detect due to the proximity of bone. In some circumstances, ischemia and/or infarcts may be challenging to detect due to the subtlety of intensity and texture changes. Areas of ischemia and/or infarcts in the brain may appear in CT images as areas of slightly lowered intensity. There may be a loss of distinction between grey matter and white matter.
Some examples of subtle stroke signs are listed as a) to e) below:—
a) Low density in insular cortex due to acute infarct.
b) Loss of differentiation of basal ganglia. Lentiform nucleus lost on right side.
c) Loss of grey/white matter in acute right middle cerebral artery (MCA) infarct.
d) Dense vessel (MCA).
e) Old ischemic change.
In some circumstances, if a naïve classifier were to be used to detect subtle stroke signs, it may be the case that normal calcification of arteries could be confused with abnormal dense vessel signs.